When a de-DE culture is applied the 1,1 should be parsed as a number. On the other hand the 1.1 (with a dot) should be parsed as 01.Jan. Currently, both values (1,1 and 1.1) are parsed as datetime. Decline reason: This is reproducible only if the cell was previously formatted as DateTime. In this case the separator is not taken into account which is expected. The same behavior can be observed also in Excel.